Drought across the midwestern and southern US has left the Mississippi River with such low water levels that saltwater from the Gulf of Mexico is creeping upriver in Louisiana, which could affect the drinking water of thousands of residents in the next few weeks.
For those who rely on the Mississippi River for drinking water, the saltwater intrusion is a potential health risk, as high concentrations of salt in drinking water may cause people to develop increased blood pressure and corrode drinking water infrastructure.
Officials are expected to give an update on the situation later on Friday.
The saltwater has already entered the drinking water of communities south of New Orleans – from Empire Bridge to Venice, Louisiana – making the water undrinkable for about 2,000 residents and causing water outages at local schools. As the saltwater moves upriver, it could affect the drinking water for another 20,000 people in Belle Chasse. After that it could reach the drinking water intake for the New Orleans community of Algiers, across the river from the French Quarter.
With no significant rain in the forecast, experts warn the saltwater could reach parts of New Orleans by 10 October, said Matt Roe, a spokesperson for the US army corps of engineers, New Orleans district. “The 28-day river forecast coupled with the rain is just not enough to make a major impact on the river down here,” he said.
On Friday at 3pm central time, the Louisiana governor’s office of homeland security and emergency preparedness is expected to hold a press conference at the Convention Center in New Orleans, where a website will be announced that will have centralized information about how local water systems are being affected.
To slow the progression of the saltwater, the army corps of engineers constructed an underwater barrier in downriver from New Orleans in July, Roe said. The mouth of the Mississippi River is below sea level. Because saltwater is denser than freshwater it is moving underneath the freshwater along the bottom of the river in a wedge shape.
The barrier was intended to slow the upstream movement of the saltwater, but the salt wedge has overtopped the barrier. Similar barriers were constructed in 1988, 2012 and 2022. This is the first time the barrier has needed to be built in back-to-back years. Last year, the barrier wasn’t overtopped, he added.
The corps of engineers is now building the underwater barrier higher near the banks of the river, but will not raise the barrier in the middle of the river to prevent blocking ship traffic. “Our estimates say that adds about 10 to 15 days’ delay of saltwater progressing up river to allow the city to work on their mitigation plans,” Roe said.
Communities along the river are keeping a close eye on the upstream movement of the saltwater wedge and testing the salinity levels near their water system intakes, said Dr Joseph Kanter, the state health officer and medical director for the Louisiana department of health. “Everyone along the river knows where the wedge is and when it’s approaching. That’s not going to be a surprise,” he said.
While salt is not a federally regulated contaminant, it could be a health concern for people who are on low salt diets and for those who are pregnant. The World Health Organization’s drinking water guideline suggests that 200mg of sodium a liter is the threshold at which most people will not want to drink the water because of taste. When saltwater is pumped through a water distribution system it can cause pipes to corrode, potentially leaching heavy metals from the pipes and pipe fittings into drinking water.
But it is difficult to predict which metals might leach from pipes, as distribution systems are all different and some do not have full maps of their systems. “So, a hallmark of the response is going to be frequent testing of the water that is going through the water systems distribution network,” Kanter said.
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The corps of engineers is exploring barging river water from upriver to areas being affected by the saltwater intrusion and smaller communities south of Louisiana are sourcing reverse osmosis devices capable of desalinating water, Kanter said. But those measures would probably not be able to replace the amount of water used by New Orleans, with a population of nearly 370,000 people.
Kanter reiterated that the current estimates are worst-case scenarios.
Multiple days of rainfall in the Missouri and Ohio River Basins would be necessary to increase the freshwater flow of the Mississippi River, said Julie Lesko, a senior service hydrologist with the National Weather Service New Orleans/Baton Rouge office. “When we look at what could happen over a two-week period we’re not seeing anything significant that would make its way down river to alleviate the problems,” she said. “Even if we got rainfall here that would significantly help our drought locally, that wouldn’t necessarily help the water conditions on the river itself.”
Coastal communities across the US are facing similar challenges with saltwater intrusion, said Allison Lassiter, an assistant professor at the University of Pennsylvania focused on urban water management. “One of the questions a lot of water managers are going to have is how do we diversify our water system to think about other places to get water from so they’re not totally reliant on the Mississippi, for example,” she said. “That’s not easy, because you need to find water that’s not being used.”
Desalination systems have limitations because they are expensive and don’t produce a lot of water. “This will be a difficult nut to crack,” she said.
Sea level rise will make the conditions that allow saltwater intrusion into the Mississippi River more likely in the future, said Soni Pradhanang, an associate professor of hydrology and water quality at the University of Rhode Island. Climate change is also expected to exacerbate droughts by making them longer and more frequent. “We’re only going to see this happening more,” she said. “Sea level rise will lead to increased salinity as more of this seawater pushes up into the estuaries and inland.”
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